It is known to remove limbs from trees by encircling the tree trunk or bole with curved cutting blades and either moving the curved blades along the length of the tree, or pulling the tree longitudinally through the curved blades. My prior U.S. Pat. Nos. 4,749,012, 4,899,794, and 5,515,895, each of which is incorporated in its entirety herein by reference, describe self-aligning limb-stripping devices for delimbing trees in which curved cutting and limb stripping levers having cutting blades are carried by a rectangular support frame supported for pivotal movement in both vertical and horizontal planes so that the limb stripping blades are automatically maintained in proper alignment with respect to the longitudinal axis of the tree as the tree is drawn longitudinally through the device in a generally horizontal orientation. A pair of curved limb stripping levers having curved cutting blades are spaced about the longitudinal axis of the device and are pivotable toward and away from each other for engaging and disengaging a tree bole. The limb stripping levers and blades are positioned and configured to substantially encircle a tree bole disposed in the device, except for the bottom portion of the tree bole for which a fixed bottom cutting blade is provided for removing limbs therefrom.
The delimbing devices disclosed in the aforementioned patents are relatively inexpensive to manufacture and maintain, and are highly effective and efficient for removing limbs from trees having a bole diameter of up to about 14 inches. However, in certain applications, trees having bole diameters of up to about 24 inches must be delimbed. For these larger trees, the curved limb stripping levers and cutting blades are not capable of encircling the uppermost portions of the tree bole and, consequently, limbs on these uppermost portions are not removed by the device.
To handle such larger trees effectively and efficiently, I have developed an improved delimbing device described in my co-pending U.S. patent application Ser. No. 09/013,158 entitled "Tree Delimbing Device" and filed Jan. 26, 1998. The delimbing apparatus described in the '158 patent application employs two pairs of curved limb-stripping levers and a fixed bottom cutting blade for removing limbs from a lower portion of the trunk. The two pairs of limb-stripping levers work in tandem to strip limbs from the top and upper side portions and from the upper side portions and lower side portions of the tree, and are pivotable to accommodate a wide range of tree diameters. The device is highly effective at stripping limbs from trees having trunk diameters of from about 4 inches up to at least about 26 inches. It has been found, however, that particularly when the bottom cutting blade encounters a limb that joins the trunk at a knot having a large diameter, the bottom cutting blade tends to cut the limb off at the base of the knot closest to the trunk. This cutting path through the limb can be substantially longer than the axial distance through the limb a short distance outward of the trunk. Consequently, the bottom cutting blade must cut through a greater limb thickness than it would have to if it were able to cut the limb a short distance outward of the trunk. This effect is particularly disadvantageous because when the butt end of the tree is grasped in the grappler of a knuckle boom loader and placed into the device, the largest limbs of the tree tend to cause the tree to rotate so that the largest limbs are at the bottom of the tree. Thus, the largest cutting distances tend to be experienced by the fixed bottom cutting blade. In some cases, this can result in damage to the bottom cutting blade.
Furthermore, when a crooked tree is pulled through the limb-stripping device, in some cases the bottom cutting blade can dig into a crooked portion of the trunk and thus impede free movement of the tree through the device. Crooked trees can also result in large forces being imposed on the bottom cutting blade, which can damage the blade.